1. Field of the Invention
The present invention relates to a backlight unit which illuminates a liquid crystal panel from its rear surface, in which display devices for specifying a display pattern corresponding to transmission/non-transmission or transparent/scattering state of each pixel are arranged.
2. Description of the Related Art
In recent years, a liquid crystal display unit using TFT-type liquid crystal panel or STN-type liquid crystal panel has been commercialized around mainly color notebook personal computer (PC) in the OA field.
Such a liquid crystal display unit has employed a method in which a light source is disposed in the back (observer's side) of the liquid crystal panel, which is illuminated with light from this light source, called backlight unit method.
As the backlight unit employed in this kind of the backlight unit method, if roughly classified, “light guide method” (so-called edge light method) in which light from a light source lamp such as a cold cathode tube (CCFT) is reflected multiply within a flat light guide plate composed of acrylic resin having excellent optical transparency and “direct type” using no light guide plate are available.
As the liquid crystal unit mounted with a light guide method backlight unit, for example, the one shown in FIG. 1 is generally known.
A liquid crystal panel 72 sandwiched between polarizing plates 71, 73 is provided on the top and a substantially rectangular light guide plate 79 composed of transparent base material such as polymethyl methacrylate (PMMA) or acrylic is provided on the bottom while a light scattering film (scattering layer) 78 is provided on the top face (light outgoing side) of the light guide plate.
A scattering reflection pattern portion for scattering and reflecting light introduced to the light guide plate 79 effectively to be uniform in the direction of the liquid crystal panel 72 is provided on the bottom of this light guide plate 79 by printing (not shown) and a reflecting film (reflecting layer) 77 is provided on the bottom of the scattering reflection pattern portion.
The light guide plate 79 is provided with a light source lamp 76 at a side end portion thereof and a lamp reflector 81 having a high reflectance is provided such that it covers the rear face side of the light source lamp 76 in order to impinge light from the light source lamp 76 effectively into the light guide plate 79. The scattering reflection pattern portion is formed by printing a mixture of white titanium dioxide (TiO2) powder dissolved in transparent adhesive agent solution in a predetermined pattern, for example, a dot pattern followed by drying so as to supply light incident upon the light guide plate 79 with directivity to introduce the light to the light outgoing face side, thereby achieving high brightness.
Further, recently, it has been proposed to provide prism films (prism layer) 74, 75 having light condensing function between the scattering film 78 and the liquid crystal panel 72 as shown in FIG. 2 in order to achieve high brightness by improving light use efficiency. The prism films 74, 75 concentrate light sent from a light outgoing face of the light guide plate 79 and scattered by the scattering film 78 highly effectively onto an effective display area of the liquid crystal panel 72.
However, in the unit shown in FIGS. 1 and 2, control of view angle depends only on the scattering property of the scattering film 78 and that control is difficult to do, so that there is such an inevitable characteristic that a central portion on the front side of the display is bright while it becomes darker as it goes to the peripheral portion. Thus, reduction of brightness when the liquid crystal display face is seen from sideway is large thereby reducing use efficiency of light.
In the unit using the prism film shown in FIG. 2, not only is the reduction of the amount of light due to absorption of the film large but also cost is increased by an increase in the number of members, because two prism films are necessary.
On the other hand, the direct type is employed by a display unit such as a large liquid crystal TV which disables use of the light guide plate.
As the direct-type liquid crystal display unit, the one shown in FIG. 3 has been generally known. The liquid crystal panel 72 sandwiched between the polarizing plates 71, 73 is provided on the top and then, light emitted from the light source 51 composed of a fluorescent tube or the like and scattered by an optical sheet like a scattering film 82 is gathered to an effective display area of the liquid crystal panel 72 highly efficiently. To use the light from the light source 51 effectively as illumination, a reflector 52 is disposed in the back of the light source 51.
However, also in the unit shown in FIG. 3, the control on view angle depends only on the scattering property of the scattering film 82 and that control is difficult to do, so that there is such an inevitable characteristic that the central portion on the front side of the display is bright while it becomes darker as it goes to the periphery. For this reason, reduction of brightness when the liquid crystal display is seen from sideway is large thereby inducing reduction of the use efficiency of light. Further, in the case of using the prism film, two pieces of the prism films are needed, so that not only is reduction of the quantity of light due to absorption of the film large, but also cost is increased due to an increase in the number of members.
If an interval of the light sources 51 is too large, unevenness in brightness likely occurs on the screen and the number of the light sources 51 cannot be reduced, thereby inducing increases in consumption power and cost.
In such a liquid crystal display unit, light weight, low consumption power, high brightness and thin structure are demanded strongly as market needs and accompanied by this, the backlight unit to be mounted on the liquid crystal display unit is demanded to have properties of light weight, low consumption power and high brightness.
Particularly, in the color liquid crystal display unit being developed progressively in recent years, the panel transmission ratio of the liquid crystal panel is extremely lower than a liquid crystal panel corresponding to monochrome and thus, it is indispensable to improve the brightness of the backlight unit in order to obtain the low power consumption of the unit itself.
However, the above-described conventional unit cannot meet the demands for high brightness and low power consumption sufficiently, and a user demands for development of a backlight unit which can realize a liquid crystal display unit having properties of low price, high brightness, high display quality and low power consumption.
In view of the above-described circumstances, this applicant has proposed a liquid crystal display unit having a liquid crystal panel and light source means for illuminating this liquid crystal panel with light from the rear side, this light source means including a lens layer for introducing light from the light source to the liquid crystal panel and the liquid crystal display unit further including a light shielding portion containing an opening in the vicinity of the focal plane in the lens layer, as described in for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-284268.
The aforementioned Jpn. Pat. Appln. KOKAI Publication No. 2000-284268 has disclosed a structure in which a lens sheet having the light shielding portion is disposed between the liquid crystal panel and the backlight unit and in FIGS. 4 to 6, the lens sheet has a uneven structure in which the lens portion is constructed on the liquid crystal side.
As for the operation and effect of interposing the lens sheet, this has an uneven structure in which the scattering property possessed by light emitted from the light guide plate is modulated by the lens action so as to construct a lens portion on the liquid crystal panel side.
The operation and effect of interposing the aforementioned lens sheet exists in that lights can be emitted toward the liquid crystal panel side by modulating the scattering property possessed by light emitted from the light guide plate by the lens action.
Additionally, due to formation of the light shielding portion having an opening portion at a specific location, the quantity of light incident on pixels of the liquid crystal panel can be increased selectively, so that the use efficiency of the backlight is improved and further, the view field area of display light can be controlled by controlling the shape of the opening.